Stepper motor devices may be divided into rotating and reciprocating step devices. A synchronous motor is one example of a single-phase rotating step device and a common stepper motor is an example of a two-phase rotating step device. A single-phase stepper motor device comprises a group of magnetic circuit components, namely, a rotor, a coil, a shell or stator core and a magnet.
Stepper motor devices have a simple structure and a certain control precision, being applied broadly, such as in driving and controlling systems. In low power applications, a claw pole structure is generally used. The magnetic field produced by the coil of the motor varies alternately.
Stepper motor devices are commonly divided into single-phase and multi-phase, wherein a single-phase stepper motor device comprises a stator, a coil and multiple magnets of alternate polarities, and a multiphase step device comprises multiple single-phase devices. The structure of an ordinary two-phase claw pole stepper motor is shown in FIG. 1, wherein it comprises a claw pole stator 101, a coil 102, a magnet 103, and a rotor 104. In the radial direction of the motor, the coil 102 is at the outer surface of the poles of the stator 101, and the magnet 103 is at the inner surface of the stator and fixed to the rotor 104. The magnet is formed as a ring which is smaller than the coil, and has a large number of magnetic poles. Thus, it is quite difficult to magnetize the magnet.
A magnetic field structure of the same polarity is disclosed in U.S. Pat. No. 3,356,876, wherein its salient pole is constructed by a laminated core, and the core rotates with the magnet being stationary; for inner rotor motors magnetizing in radial direction, an air gap is provided between the internal surface of the magnet and the stator core; because the influence of the thickness in radial direction of the magnet, the external diameter of the air gap decreases, and the energy generated through the air gap by the device has little change, so the output force of the device decreases. At the same time, for devices with smaller external diameter, the magnet thereof is correspondingly small, and needs to be magnetized as a whole to form alternate magnetic poles uniformly distributed at the inner surface of the magnetic ring; because it is hard to push the magnetizing fixture into the inner hole of the magnet, it is more difficult to magnetize.